Molecular doping of organic semiconductors by either strong electron donors or acceptors has been demonstrated to provide advantages in thin film devices. The addition of dopants can increase the hole or electron density depending on their nature and modulate the Fermi level (EF).
Inorganic materials such as silicon are generally used for charge transport applications. Organic materials, particularly polymers are being studied for these applications for some time now.
Semiconducting polymers are poised to transform the scenario of today's electronics and display technology. Intensive research in the last two decades has been stimulated by the prospect for low-cost fabrication of devices with reasonable stability and performance. Although the field of semiconducting and conducting polymers has generated a huge amount of literature, the potential for conduction in polymeric materials itself remained unrecognized for a long time.
Further in thin film devices, n-type doping has been found to increase the charge carrier mobility and improve the air stability of the device. To donate electrons to an organic semiconductor, the dopant must have highest occupied molecular orbital (HOMO) level above the lowest unoccupied molecular orbital (LUMO) of the semiconductor. Such a HOMO energy level is vulnerable for oxidation due to low lying oxygen energy level (−5.2 eV). This complicates the device fabrication process and limits the use of dopants in organic filed effect transistors (OFETs). Use of dopants such as tetrathianaphthazene with low ionization energy has been attempted. However, they are not strong enough dopants to appreciably increase the charge carrier mobility of the semiconductors. Cationic salt precursors such as crystal violet and pyronin B have also been used as dopants. Another approach is the use of organometallic sandwich dimers as n type dopant. The dimer cleaves into monomer radicals upon heating, which inject electrons into the semiconductor resulting in n type doping. Recently, Peng Wei et al. in J. Am. Chem. Soc., 2010, 132 (26), pp 8852-8853 have been employed neutral radical forming (4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl)dimethylamine (N-DMBI) to n dope [6,6]-phenyl C61 butyric acid methyl ester (PCBM). The n doping increased the conductivity of the PCBM by four orders. More recently, Peng Wei et al. in J. Am. Chem. Soc., 2012, 134 (9), pp 3999-4002 describes the cationic analogue of N-DMBI, to increase the conductivity of fullerene C60 to 5.5 S/cm. However, said dopant didn't improve the field induced charge carrier mobility of C60.
Perylene-3,4,9,10-tetracarboxylic acid diimides (perylene diimides, PDIs) or Perylenebisimides (PBIs) are well known n type materials, which provide myriad of opportunities for installing functional moieties. The self-assembly, electronic and optical properties of PBIs can be modulated by functionalization at imide nitrogen.
Recently, the applications for PDI or PBI derivatives have emerged in areas including organic electronics like organic photovoltaic devices and field-effect transistors. Therefore the synthesis and physical properties of PDI derivatives become more important.
There are ample literature which describe the PDI or PBI derivatives, for example Pradip K. Sukul et al. in Chem. Commun., 2011, 47, 11858-11860 reported unique and spontaneous formation of hydrogels of perylene derivatives with melamine further, this article provides synthesis of N,N′-Di-(phenyl-3,5-dicarboxylic acid)-perylene-3,4:9,10-tetracarboxylic acid diimide (PI) from perylene-3,4:9,10-tetracarboxylic dianhydride, 5-aminoisophthalic acid and imidazole (85% yield).
Bo Gaoa et al. in supramolecular chemistry 19, (3), 2007 pg. 207-210 discloses supramolecular self-assembly, where a pyridyl-substituted perylene bisimide dye (DPyPBI) axially binds to zinc phthalocyanine (ZnPc). Additionally Zinc (II)-selective ratiometric fluorescent probe based on perylene bisimide derivative is reported in Luminescence. 2011 May-June; 26(3):214-7.Epub 2010 by Zhao Y et al. The palladium complexes of perylene diimides (PDI) is reported in Inorg Chem. 2007 Jun. 11; 46(12):4790-2. Epub 2007 May 16 by Weissman H, et al.
Further donor-acceptor complex formation in evaporated small molecular organic photovoltaic cells is reported by Diana K. Susarova in Solar Energy Materials & Solar Cells 94 (2010) 803-811 wherein perylene diimide Py-PDI and naphthalene diimide Py-NDI possessing chelating pyridyl groups form self-assembled coordination complexes with ZnPc in solution and co-evaporated solid blends. Further it discloses perylene-3,4,9,10-tetracarboxylic acid dianhydride was mixed with freshly distilled quinoline, 3-picolylamine and Zn(OAc)2.H2O.
Synthesis, physical properties, and use of perylene-3,4,9,10-tetracarboxylic acid diimides is demonstrated by Chun Huang in organic electronics, in J. Org. Chem., 2011, 76 (8), pp 2386-2407. Also CN101949026 relates to a method for preparing a perylene polyimide derivative film useful in the field of photoelectric materials.
In view of foregoing, there is still a need to develop ‘radical containing PBIs based devices’ that works at low operating voltages with high charge carrier mobility, which would be a step forward in the direction of commercial exploitation of OFETs.